Two-stage reforming with intermediate fractionation



Oct. 3, 1961 W. W. HAMILTON TWO-STAGE REFORMING WITH INTERMEDIATE FRACTIONATION Filed Sept. 6, 1956 3 Sheets-Sheet 1 INVENTOR W2k/m1 W.' Ham /aw Oct. 3, 1961 w. w. HAMILTON TWO-STAGE REFORMING WITH INTERMEDIATE FRACTIONATION Filed Sept. 6, 1956 3 Sheets-Sheet 2 mww SES mm Oct. 3, 1961 w. w. HAMILTON TWO-STAGE REFORNIING WITH INTERMEDIATE FRACTIONATION Filed Sept. 6. 1956 3 Sheets-Sheet 3 3,002 916 TWO-STAGE REFORMIN WITH INTERMEDIATE FRACTIGNATION Winton W: Hamilton, Pitman, NJ., assignor to Socony Mobil OrlCompany, Inc., a corporation of New York Filed Sept. 6, 1956, Ser. No. 608,294 3 Claims. (Cl. 208-64) The present invention relates to the production of high octane rating gasoline with improved yields and, more particularly, to reforming gasoline at high pressures in a rst stage and at lower pressures in a second stage.

Low octane rating gasoline is a mixture of hydrocarbons having 4 or more car-bon atoms in the molecules, classified as paraiins, olelins, naphtheles and aromatic hydrocarbons. The `hydrocarbons having 4 carbon atoms will, in a modern refinery, be the normal butane 'remaining from alkylation and are of little importance 1n this invention. Conventional catalytic reforming converts the pentanes and hexanes to hydrocarbons having a higher octane rating than the original C5 and C6 hydrocarbons but at a yield which is not as economic as conversion by other methods. ln conventional reforming, the reactions of the C7 and heavier molecules depend on the class and molecular weight of the molecules.

The heptane and heavier fraction of a gasoline from a Mid-Continent crude has the following composition:

Hydrocarbon type: Volume, percent The olelins will usually -be converted to parans either in a pretreater or on the rst contact with reforming catalyst. Thus the charge to the reformer can be considered to be mainly paraiins, naphthenes and aromatics.

The aromatic hydrocarbons have a high octane number and are changed very little if any during conventional catalytic reforming. The naphthenes are converted almost quantitatively to aromatic hydrocarbons under reforming conditions. The reactions of the parailin hydrocarbons depend on the reforming conditions, and the molecular Weight of the paraftins. The parains range from C7 to about C12 usually and in catalytic reforming are either dehydrocyclized to aromatics or hydrocracked to lower molecular weight hydrocarbons. High pressure catalytic reforming favors hydrocracking whereas low pressure reforming favors dehydrocyclization.

For the higher molecular weight paraliins, hydrocracking is preferred over dehydrocyclization. The products of hydrocracking are likely to be in the gasoline boiling range. Por example, hydrocracking a C10 paraihn into two C5 molecules will produce a yield about 120 vol. percent and an increase in octane rating of about 100 units. When a paraiin is reformed by dehydrocyclization to the corresponding aromatic hydrocarbon, the aromatic hydrocarbon produced has a boiling point higher than the original paraflin. Consequently, when dehydrocyclizing a high molecular lweight paraffin, say a C12 parain, the produced aromatic often has a boiling point too high to be included in the reformed gasoline.

For the lower molecular weight parail'lns, dehydro cyclization is preferred over hydrocracking. The prod- States PatentfO 3,002,916 Patented Oct. 3, 1961 ICC cluded to only a limited extent. However, if a low molecular weight paraffin is dehydrocyclized to an aromatic, the aromatic has a very high octanenumber and has a low enough boiling point to be included in the gasoline. For example, if a C7 paraffin is dehydrocyclized to toluene, the toluene is well within the normal gasoline boiling range.

Therefore, the preferred reactions are: hydrocracking `for the higher molecular weight paramos, and dehydrocyclization for the lower molecular weight parains'. This would apparently call for reforming the high molecular weight paraffns at high pressure and the low molecular weight paratlins at low pressure. However', it has been found that the Vhigh molecular weight parains crack more rapidly than the low molecular weight paralins. Therefore a mixture of high and low molecular weight paratins can be reformed at high pressure and a moderate severity, thereby -hydrooracking most of the high molecular weight paraftins while hydrocracking the low molecular weight paraflins to only a moderate extent. The remaining paramns can then be subjected to low pressure reforming where the remaining low molecular weight parathns are dehydrocyclized to aromatica with hydrocracking being minimized.

While hydrocracking of low molecular weight paraifms has been minimized in the high pressure reformer by'operating at moderate severity and' in the low presucts of hydrocracking are likely to be outside the gasoi the C3 paraiiin in gasoline and the C4 paran'can be in` u sure reformer by the low pressure itself, some hydrocracking of low molecular weight paraftins will occur in both reformers. Therefore, the lowest molecular weight paraihns presentV in a full boiling range gasoline can be removed and lcharged to a more economic process rather than being charged to reforming where some hydrocracking will occur. For example, the C5, C6, and possibly the C7 hydrocarbons could be removed by distillation and charged to an isomerization unit rather than being charged to the high pressure reformer. Low molecular weight hydrocarbons will be produced in the high pressure reformer so the C5, C@ and possibly the C7 hydro,- carbons can `be removed from the reformate from ythe high pressure reformer before charging the heavier portion to the low pressure reformer. VVThe lighter portion removed by distillation can go to the isomerization unit.

Illustrative of the preferential cracking of high molecular weight parains and the slight or moderate cracking of low molecular weight paraiins under high severities are the data presented in Table I.

TABLE I Charge- Ex. 1 Ex. 2 `l'lx. 3

Severity A B O Pressure, p.s.l.g- 500 500 500 Reactor Temp.V oi Space Velocity 940 940 940 V./hr. 3 2 1 Hydrogen to naphtha Mol Ratio 10 10 10 Res. O.N+3 ce. TEL 76 90 100 103 Hydrocarbon: f Y l l Parans, vol. percent. 46. 5 51:7 40.6 30.8 Aromatics, vol. percent 6. 7 32.8 4l. 6 41. 8 Naphthenes, vol. percen 43:8A 9.0 Qtgherxy yol. percent. 3.0 2.0 `0. 6 0.4

.Barattin Distribution: i 0.0 3. 0 6. 5 7. 5 3. 6 6. 2 8.9 10.0 10.6 13. 2 11. 5 8. 4 12.4 13.8 9.1-v` 4.0 l0. 0 8. 9 3. 4 0. 9 6.2 4..6 1. 2

In Table II data are presented showing the yield of aromatic hydrocarbons from parains when reforming at various pressures. The severity of the reforming conditions can be sucient to convert the paraiiins charged completely to aromatic hydrocarbons or lower boiling paraiins. The data establishes that the lower the pressure, the greater the fraction of parans converted to aromatichydrocarbons. However, the lower the pressure, the poorer the catalyst life. Consequently the determination of the lowest pressure to be used in the low pressure or second reformer of the present invention is determined by overall economics considering as factors, yields, catalyst cost, investment, and other operating costs.

TABLE II Pressure, p.s.l.g 100 200 350 500 Reactor Temp., percent 950 950 950 95() `Space Velocity, v./hr.lv 2 2 2 2 Hydrogen to naphtha mol ratio 10 10 10 l0 Yield of Aromatlcs,1 Vol. of charge 42 32 1o 8 l Balance oi parains hydrocracked to lighter parains.

In Table III are presented data showing the yields obtained when treating a C5+ gasoline in accordance with the principles of the present invention including isomeriza tion of the C5 and C5 hydrocarbons.

TABLE III Total low octane rating gasoline Hydrocarbons Barrels/Day Treatment Isomerzed. Do. High Pressure Reforming.

Product from high pressure reforming Hydrocarbon Barrels/Day Treatment Isomerized. Do. Low Pressure Reforming.

Product from low pressure reforming Hydrocarbon Barrels/Day Treatment Isomerlzed.

Do. v Y Gasoline (substantially pure aromatica).

Products from isomerizaton Thus, from 11,240 barrels of C5| gasoline having a Research O.N.I3 cc. TEL of 76 there was produced by the process of the present invention 9090 barrels of gasoline having a Research O.N.{3 cc. TEL of 110. In contrast, reforming the same gasoline to Research O.N.|3 cc. TEL in accordance with prior art processes yields only 6080 barrels of gasoline of required octane rating. In other words, the process of the present invention provides a yield of about 80.7 volume percent ofthe charge while prior art processes provide yields of only about 54 volume percent of the charge. Furthermore, when the C5 and C6 hydrocarbons produced in the high pressure reformer are charged to the low pressure reformer, in contrast to the principles of the present invention, about 600 barrels per day of hexane and about barrels per day of pentanes are lost by hydrocracking to gas.

FIGURE l is a simplified ow diagram illustrative of an operation producing the result presented in Table III.

The simplified flow diagram FiGURE 1 illustrates the preferred embodiment of the present invention. A low octane number gasoline is iirst pretreated to remove sulfur compounds, and/or nitrogen compounds and other contaminants which have a deleterious eiect upon the catalyst, cause corrosion or for other reasons preferably are removed from the charge stock. The pretreated gasoline is then dehexanized, i.e., C5 and lighter hydrocarbons are removed as an overhead. The bottoms, i.e., C7 and heavier hydrocarbons are then reformed at high pressures of the order of about 300 to about 750 p.s.i.g. under conditions favoring hydrocracking of the paratiins in the dehexanized charge and dehydrogenation of .the naphthenes.

The efuent of the high pressure reformer is dehexanized and the C7 and heavier hydrocarbons are reformed at low pressures ofthe order of about l0() to about 300 p.s..g. under conditions favoring aromatization of the low boiling parafns. The eiuent from the low pressure reformer is dehexanized. The C7 and heavier hydrocarbons of the low pressure reformer effluent are the aromatic component of the gasoline blend. The C6 and lighter hydrocarbons separated from the charge stock, from the high pressure reformer eluent, and from the low pressure reformer eluent preferably are combined and debutanized. The C4 and lighter hydrocarbons taken as overhead in the debutanizer are used to pressure the blend gasoline, as liquefied petroleum gas and for various other purposes. The debutanized fraction is then treated as by distillation to separate C6 and lighter. The dehexanized fraction comprising C7 and heavier hydrocarbons are either admixed with the charge to the low pressure reformer or passed through an adsorber in conjunction with the eiuent from an isomerization reaction to which reference is made hereinafter.

The overhead of the dehexanizer comprising C6 and C5 hydrocarbons is then treated to remove pentanes. The pentanes pass to a pentane splitter in which the isopentane is taken overhead and the normal pentane is the bottoms fraction.

The bottoms of the depentanizer ilows to a C6 splitter where the isohexane is taken as overhead and the normal C5 parains and methylpentane form the bottoms fraction.

The bottoms from the C6 splitter and the bottoms ofthe .C5 splitter are isomerized. The efuent of the isomerization reaction is fractioned to separate the normal C5 and C hydrocarbons from the isoparafns having 5 and 6 carbon atoms.

The isopentane taken as overhead from the C5 splitter and the isohexane taken as overhead from the C5 splitter are blended with the aromatic bottoms of the dehexanized etiiuent from the low pressure reformer to form the gasoline blend.

Suitable catalysts and operating conditions for high pressure and low pressure reforming are listed in Table IV.

75y Table IV is Yillustrative. and not exclusive.

TABLE Iv High pressure reform er CONDITIONS FAVORING HYDROCRACKING HEAVY (010+) PARAFFINS, AND DEHYDROGENATING NAPHTHENES Low pressure reformer CONDITIONS FAVORING AROMATIZATION OF LOW BOIL- ING, C7-O1n PARAFFINS AND DEHYDROGENATION OF NAPHIBENES Hydro- Reactor Av. Reac- Space Catalyst gen to Pressure, tor Temp., Velocity, oil, mol p.s.i.g. F. v./hr./v.

ratio 1-10 50-200 750-1, 000 0. 1-2 1-l0 50-200 80G-1, 050 0. 1-2 Pt group on Alumina 1-15:1 1D0-300 SOO-1, 000 0. 1-5

In FIGURE 2 is illustrated by a more detailed ow sheet high pressure and low pressure reforming with removal of C5 and C6 hydrocarbons from the eluents of both reactors employing a platinum group catalyst in both the high pressure reformer and the low pressure reformer.

A full boiling range naphtha pumped from a source not shown at the pressure existing in high pressure reformer 29 iiovvs through line 10 to absorber Il. A gas containing C1 to C-lhydorcarbons and hydrogen flows through line 22 under control of valve 23 to absorber lll. The amount of gas flowing .through line 22 is regulated by the pressure in gas separator 34 and is about equivalent to the net make of gas in reformer 29. The naphtha contacts the gas in absorber i1 and extracts the heavier hydrocarbons from the gas. The gas stripped of .these hydrocarbons flows from absorber 11 through line 12 to the refinery fuel system.

The charge naphtha enriched with the hydrocarbons absorbed in absorber il iiows along lines i3 and 14 to heat exchanger i5 where it is in indirect heat exchange with the erlluent' from reformer 29. The heated, enriched naphtha flows from heat exchanger 15 through lines 16 and 17 to coil i3 in heater i9 where it is heated to reaction temperature or to a temperature such that, when mixed with recycle gas heated to a temperature above reaction temperature inthe mol ratio of 1-10 mols hydrogen per mol of naphtha to form a charge mixture, the charge mixture has a reaction temperature of about 800 to about 105 0 F.

The heated naphtha ilows from coil 13 through line 20 to line 21. Recycle gas produced as hereinafter described is pumped by compressor 24 through line 25 to coil 26 in heater 27. The hydrogen-containing recycle gas is heated in coil 26 to at least reaction temperature and preferably higher thereby reducing the temperature to which the naphtha is heated and concomitantly vreducing thermal conversion. The heated hydrogen-containing recycle gas Hows from coil 26 through line 23 to line 21 where it is mixed with the heated charge naphtha in the mol ratio of about l to about l0 mols of hydrogen per mol of naphtha to form a charge mixture having a temperature of about 800 to about 1050 F. and approximately that of the reaction temperature in high pressure reformer 29.

The catalyst employed in high pressure reformer 29 can be any'reiorming catalyst such as group VI metal oxide on a carrier such as alumina; a mixture of group Vl and group VIImetal oxides on a carrier; a platinum group metal on a support such as alumina and in general a catalyst corn-v 6 bining dehydrogenation capabilities with hydrocracking capabilities. For the purpose of illustration a catalyst comprising about 0.6 Weight percent platinum and about 0.6 weight percent chlorine on an alumina support has been selected.

The charge naphtha is reformed under conditions favoring the cracking of the high molecular Weight paraiiins (C10-H with only mild aromatization of the paramos while dehydrogenating the naphthenes of the charge. By reforming the charge over the catalyst of the illustration to about 92-90 O.N. the foregoing results can be achieved. Reforming to 92-98 O.N. is achieved at about 350 to 750 p.s.i.g at 800 to 1050 F. employing a liquid space velocity of 1-6 volumes of liquid charge per volume of catalyst per hour.

The eliuent of high pressure reformer 29 flows through line 30 to heat exchanger 15 previously described and thence through line 31 to cooler 32 Where the efliuent is cooled to a temperature such that most of the C5 and heavier hydrocarbons liquefy at the pressure of reformer 29. The mixture of the uncondensed portion of the eliuent and the condensed portion of the eflluent ows through line 33 to liquid gas separator 34.

In liquid-gas separator 34 the uncondensed portion of the eliiuent from the high pressure reformer ilows through line 35 to line 36. A portion about equivalent to the net make of gas in reformer 29 ows through line 22 under control of valve 23 as previously described. The balance iiows to compressor 2d for use as recycle gas.

The condensed portion of the high pressure reformer effluent flows from separator 34 through line 37 to debutanizer 3d. In debutanizer 3S an overhead comprising C4 and lighter hydrocarbons is taken overhead through line 39 leaving as bottoms C5 and heavier hydrocarbons.

A portion of the bottoms is circulated through a reboiler comprising line 40, pump 41, heat exchanger 42 and line 43 to maintain distillation temperatures in debutanizer 38. The balance of the bottoms ows from debutanizer 35 through line 44 to heat exchanger 45 Where it is heated to a temperature at Which- C hydrocarbons are vaporized.

The heated debutanizer bottoms flows through line 46 to dehexanizer 47. In dehexanizer 47 a C5-C5 overhead is taken through line 4S preferably to an isomerization unit not shown. The bottoms comprising C7 and heavier hydrocarbons in part is circulated through a reboiler comprising line 49, pump 50, heat exchanger S1 and line 52 to maintain the volatilization temperature required in dehexanizer 47. The balance ows from dehexanizer 47 through line 53 to low pressure absorber 54.

In low pressure absorber 54 the C7 and heavier bottoms from dehexanizer 47 contact gas from low pressure reformer 70 in amount about equivalent to the net make of gas in low pressure reformer '70. The net make of gas `from low pressure reformer '70 iiows through line 55 under control of valve So yto absorber 54. In absorber 54 the heavier, C5| hydrocarbons are absorbed from the net make of gas. The gas stripped of the C5-lhydrocarbons is vented through line 57 to the renery fuel system.

The C74- dehexanizer bottoms enriched with hydrocarbons stripped from the net make gas flows from absorber 54 through line 58 to heat exchanger 59 Where the enriched dehexanizer bottoms are in heat exchange relation with the eiiiuent from low pressure reformer 70. From heat exchanger 59 the heated enriched dehexanizer bottoms `flows through line 60 to coil 61 in heater 62.

In coil 6l the enriched dehexam'zer bottoms are heated to reaction temperature or to a temperature such that, when mixed with heated recycle gas in the ratio of about 1 to 15 mols hydrogen per mol of dehexanizer bottoms to form la charge mixture, the charge mixture has a temperature approximating the reaction temperature the low pressure reformer 70 and about 800 to 1050 F.

Recycle gas obtained as hereinafter described and comprising hydrogen and C1+ hydrocarbons is pumped by compressor 65 through line V66 to coil 67 in 'heater 65. In coil 67 the recycle gas is heated to at least the temperature existing in reformer 70. The heated recycle gas ilows from coil 63 through line 69 to line 64 where it is mixed with heated enriched dehexanizer bottoms in the ratio of about 1 to 15 mols of hydrogen per mol of bottoms to form a charge mixture.

The charge mixture flows through line di. to low pressure reformer 70. In low pressure reformer 7G the dchexanizer bottoms contact a reforming catalyst comprising a dehydrogenating catalyst and a support under conditions such that any naphthenes present are dehydrogenated and all paraiiins are dehydrocyclicized with cracking being minimized. For a catalyst comprising about 0.6 weight percent platinum and about 0.6 weight percent chlorine on an alumina support the low pressure reformer is operated at a pressure of about 100 to 300 p.s.i.g., a temperature of about 800 to 1050 F., a liquid space velocity of about 0.1-6 v./hr./v. and with a hydrogen to dehexanizer bottoms mol ratio of about 1-15 :1.

The effluent from low pressure reformer '70 flows through line 71 to heat exchanger 59 previously described and thence through line 72 to cooler 73 where the low pressure reformer eluent is cooled to a temperature at which most of the C5 and heavier hydrocarbons liquefy.

From cooler 73 the liqueed and gaseous components of the low pressure reformer eiuent flow through line 74 to liquid-gas separator 75. In separator 75 the liqueed eiuent separates from the gaseous low pressure reformer effluent. The gaseous low pressure reformer effluent leaves separator 75 through line 76 through which it ows in part to compressor 65 while the net make of gas flows through line 55 to absorber 54 as previously described.

The liquefied portion of the low pressure reformer efluent iiows through line 77 to debutanizer 78 from which an overhead comprising C4 and lighter hydrocarbons is taken overhead through lines 79 and 80 to line 39.

A portion of the debutanizer bottoms comprising C5 and heavier hydrocarbons flows through a reboiler comprising line 31, pump 32, heat exchanger 83 and line 84 to maintain a temperature in debutanizer 78 high enough to vaporize C4 and lighter hydrocarbons. The balance of the debutanizer bottoms flows through line to heat exchanger S6 where the temperature is raised to that at which C6 and lighter hydrocarbons are volatilized. The heated debutanizer bottoms flow from exchanger 36 through line 87 to dehexanizer 3S.

1n dehexanizer 8S a C5-C6 overhead is taken through line 89, preferably to an isomerization unit. The bottoms comprising C7 and heavier hydrocarbons in part is circulated through a reboiler comprising line 90, pump 91, heat exchanger 92 and line 93 to maintain a temperature at which C6 hydrocarbons are volatile. The balance of the dehexanizer bottom flows therefrom through line 941 to provide a highly aromatic component of the gasoline blend. This component can be substantially pure aromatics.

The flow sheet FIGURE 2 illustrates the use of static catalyst beds in both the high pressure and the lowpressure reformers. However, the present invention is not so limited and moving bed or fluidized beds of catalyst can be used in both or either reformer. The flow sheet of FIGURE 3 illustrates the use of a static bed of catalyst in the high pressure reformer and a moving bed of catalyst in the low pressure reformer. Thus, the catalyst in the high pressure reformer can be the platinum group metal catalyst previously described while the catalyst employed in the loW pressure moving bed reformer can be a chromium oxide-aluminum oxide reforming catalyst comprising at least 70 mol percent aluminum oxide (alumina) and 18 to 30 mol percent chromium oxlde (chromia).

As illustrated in FIGURE 3 the preferred C, and heavier fraction of naphtha is pumped from a source at the pressure existing in high pressure reformer 117 through line 160 to absorber 101. In absorber 101 the C7+ naphtha charge is contacted with gas from liquidgas separator 122 liowing through line 1112 and regulated by valve 103 to the amount of the net make of gas in high pressure reformer 117. The Cq-lfeed strips C4-lhydrocarbons from the gas and is thus enriched. The stripped gas leaves the absorber 101 through line 104 yand tiows to the refinery fuel system.

The enriched Cq-lfraction flows from absorber 101 through line 105 to heat exchanger 106 where it is in heat exchange relation with the eflluent of high pressure reformer 117. From heat exchanger 106 the heated, enriched C7+ fraction flows through line 107 to coil 108 in heater 109.

In coil 108 the enriched C74- fraction is heated to a temperature such that, when mixed with heated recycle gas in the mol ratio of l to 15 mols of hydrogen per mol of (37+ fraction to form a charge mixture, the temperature of the charge mixture is that of the high pressure reformer and about 800 to l050 F.

Recycle gas comprising hydrogen and Cl-lhydrocarbons ilows from liquid-gas separator 122 through lines 123 and 124 -to compressor =112 thence through line 113 to coil 114 in heater 115. 'In coil 114 the recycle gas is heated to at least the temperature existing in high pressure reformer 117. The heated recycle gas flows from coil 11'4 through line 116 to line 111 where it is mixed with the heated enriched Cq-lfraction to form a heated charge mixture.

The heated charge mixture flows through line 111 into high pressure reformer 117. The high pressure reformer eiuent flows from high pressure reformer 117 through line 118 to heat exchanger 106 previously described and thence through line 119 to cooler 120.

In cooler 120 the high pressure reformer effluent is cooled to a temperature at which most of the C5 and heavier hydrocarbons are liquefied. The mixture of liquefied hydrocarbons and gas flows through line 121 to liquid-gas separator 122. From liquid-gas separator 122 the gaseous portion of the high pressure reformer efuent flows through line 123 to line 124. Here -a portion about equivalent to the net gas make in the high pressure reformer ows through line 1112 while the balance as recycle gas flows to compressor 112.

The liquid portion of the Ihigh pressure reformer efduent ows from separator 122 through line 12S to debutanizer 126 where C4 and lighter hydrocarbons are taken as overhead through line 127 and the C5 and heavier hydrocarbons form a bottoms.

A portion of the bottoms is circulated through a reboiler comprising line 128, pump 129, line 130, heat exchanger 131 and line 132 to maintain a temperature in debutanizer 126 at which C4 and lighter hydrocarbon volatilize. The balance of the debutanizer bottoms flows through line 133 to heat exchanger 134 where the ternperature of the debutanizer bottoms is raised to volatilizc C6 and lighter hydrocarbons. The heated debutanizer bottoms flow from exchanger 134 through line 135 to dehexanizer 136.

In dehexanizer 135 the C6 and lighter hydrocarbons are removed as overhead through line 137 preferably to an isomerizing reaction. The C7 and heavier hydrocarbons form a bottoms product. A portion of the bottoms is circulated through a reboiler comprising line 138, pump 139, line 140, heat exchanger 141 and line 142 to maintain a temperature in dehexanizer 136 at which C6 and lighter hydrocarbons are volatile. The balance of the C7+ bottoms of the dehexanizer flows through line 143 to absorber 144.

A In absorber 144 the C7| bottoms contact gas from liquid-gas separator 174 in amount about equivalent to the net make of gas in low pressure reformer 162. 'Ihis net gas make flows from liquid-gas separator 174 through lines 155 and 145 under control of valve 146. In absorber 144 the net make gas is stripped of C5| hydrocarbons. The stripped gas leaves absorber 144 through line 1117 to flow to the refinery fuel system'.

The C7+ bottoms enriched with the hydrocarbons stripped from the net make gas flows at the pressure of low pressure reformer 162 from absorber 144 through line 143. The enriched C7+ bottoms how through line 148 to heat exchanger 149 where the relatively cold C7| bottoms are in heat exchange relation with the hot eluent of the low pressure reformer. From heat exchanger 149 the heated C74- bottoms flow through line 150 to coil 151 in heater 152.

In heater 152 the C7+ bottoms are heated to a temperature such that when mixed with heated recycle gas in the ratio of about 1 to 15 mols of hydrogen per mol of 07+ bottoms to form a charge mixture the charge mixture has a temperature approximating that of the low pressure reformer and about 800 to about 105G F. The heated C7-1- bottoms How from heater 152 through line 153 to line 154.

Recycle gas containing at least 25 percent hydrogen and the balance (31+ hydrocarbons ows from liquidgas separator 174 through line 155 to recycle gas compressor 156. A portion of the recycle gas approximating the net make of gas in the low pressure reformer is'bledolf through line 145 under control of valve 146 las described hereinbefore.

Recycle gas compressor 156 pumps the recycle gas through line 157 at the pressure of the low pressure reformer to coil 158 in heater 159. In heater 159 the recycle gas is heated to at least the temperature of the low pressure reformer and preferably to a higher temperature such that the charge mixture of recycle gas and enriched C7+ bottoms is at the temperature of the low pressure reformer as described hereinbefore. The heated recycle gas at low pressure reformer pressure ows from heater 159 through line 160 to line 154 where it mixes with the heated enriched C7+ bottoms to form the charge mixture described hereinbefore. The heated charge mixture Hows through line 154 to distributor 161 in low pressure reformer 162.

A portion of the heated charge mixture iiows upwardly from distributor 161 countercurrent to the downwardly flowing particle-form reforming catalyst to ow from low pressure reformer 162 through collector 163 and line 164 under control of valve 165 to line 166. The balance of the charge mixture flows downwardly from distributor 161 concurrently with the downwardly flowing particle-form solid reforming catalyst and leaves low pressure reformer 162 through collector 167 and line 168 under control of valve 169 to line 166.

The eiuent from the upper reaction zone of low pressure reformer 162 owing through line 164 to line 166 and the etliuent from the lower reaction zone of low pressure reformer 162 tlowing through line 168 are mixed in line 166 to form a total low pressure reformer eiiiuent which flows from line 166 through line 170 to heat exchanger 149 where the total low pressure reformer eluent is in heat exchange relation with the enriched C7-lbottoms as described hereinbefore.

The total low pressure eiuent iiows from exchanger 149 through line 171 to cooler 172 where the total etliuent is cooled to a temperature at which most of the C4-lhydrocarbons condense. The cooled total efuent flows through line 173 to liquid-gas separator 174 Where the uncondensed portion of the total eluent comprising hydrogen and Cl-lhydrocarbons and equal in amount to the recycle gas in the charge mixture to low pressure reformer 162 plus the net make of gas in low pressure reformer 162 separates from the condensed portion of the total eiuent from low pressure reformer 162.

'I'he uncondensed portion of the total eluent ows from liquid-gas separator 174 through line 155 to compressor 156 and -absorber 144 as described hereinbefore. The condensed portion of the total elluent flows from separator 174 through lines 175 and 176 to debutanizer 177.

In debutanizer 177 an overhead of C4 and lighter hydrocarbons is taken through line 17S. The balance of the condensed portion of the total effluent forms a bottoms product.

A portion of the bottoms is circulated through a reboiler comprising line 179, pump 186, line 181, heat exchanger 182 and line 133 to maintain the bottoms product at a temperature lat which C4 `and lighter hydrocarbons are volatile. The balance of the bottoms flows through line 184 to heat exchanger 185 where the temperature of the debutanizer bottoms is raised to that at which C6 and lighter hydrocarbons are volatile. The heated debut-anizer bottoms iiow from exchanger 185 through line 186 to dehexanizer 187.

An overhead of C5 and lighter hydrocarbons is taken from dehexanizer 187 through line 185 preferably to an isomerization reaction. The Ibalance of the debutanizer bottoms -forms a dehexanizer bottoms.

A portion of the dehexanizer bottoms is circulated through a reboiler comprising line 189, pump 190, line 191, heat exchanger 192 and line 193 to maintain the dehexanizer bottoms at a tempera-ture at which C5 and lighter hydrocarbons are volatile. The balance of the dehexanizer bottoms is a high octane number highly aromatic product which is suitable after cooling for use as a spark ignited internal combustion engine fuel or suitable for blending as described hereinbefore.

Lt will be observed that in the flow diagrams FIGURES 2 and 3 provision has been made to heat the debutanizer bottoms prior to introduction into the dehexanizers. These heaters can be eliminated when the dehexamzers are operated at lower pressures than the debutanizers. The lower pressures in the dehexanizers will provide the required vaporization.

Thus, the present invention provides, generally, for reforming a charge stock in the presence of a reforming catalyst having dehydrogenating and cracking capabilities and in the presence of hydrogen at high reactor pressures under conditions of temperature and space velocity to crack Clo-lhydrocarbons whilst dehydrogenating naphthenes to obtain a high pressure etiluent comprising hydrogen and C1+ hydrocarbons, separating hydrogen and C4 and lighter hydrocarbons from C5 and heavier hydrocarbons, separating C5 and C6 hydrocarbons from C7 and heavier hydrocarbons, reforming smid C7 and heavier hydrocarbons in the presence of a reforming catalyst having dehydrocyolizing capabilities and in the presence of hydrogen at a pressure lower than the aforesaid high reactor pressure and under conditions of temperature, pressure and space Velocity to dehydrocyclicize said C7 and heavier parain hydrocarbons, to dehydrogenate C7 and heavier naphthenes and to avoid substantial cracking of said hydrocarbons to produce a low pressure eiluent comprising hydrogen and C1 and heavier hydrocarbons, separating hydrogen and C1 to C4 and lighter hydrocarbons from a fraction comprising C5 and heavier hydrocarbons and separating C6 land lighter hydrocarbons yfrom C7 and heavier hydrocarbons to obtain a product boiling in the gasoline boiling range containing C7 and heavier hydrocarbons which can be substantially devoid of non-aromatic hydrocarbons. In the preferred form the C5 and C5 hydrocarbons separated from the C7 and heavier hydrocarbons are isomerized to provide a high octane number component in the gasoline boiling range.

I claim:

v1. A method of producing high octane gasoline which comprises reforming low octane gasoline containing principally C', and heavier hydrocarbons in the presence of hydrogen and a reforming catalyst at relatively high pressures of at least 300 p.s.i.g. but below 750 p.s.i.g. and at a temperature in the range 750 to 1050" F. and a space velocity in the range 0.1 to 6 v./hr./v. to crack C15 and heavier hydrocarbons whilst dehydrogenating naphthenes to obtain 4a high pressure reaction zone eiuent comprising hydrogen and Cl-lhydrocarbons, separating hydrogen :and Cl-C hydrocarbons from said high pressure zone eliluent to obtain a low pressure zone charge stock comprising principally C7 and heavier hydrocarbons, reforming said low pressure zone charge stock in the presence of a reforming catalyst and hydrogen at a reaction pressure lower than the aforesaid high pressure and not exceeding 300 p.s.i.g. and reforming conditions of temperature in the range 750 to 1050 F. and space velocity in the range 0.1 to 6 v./hr./v. to dehydrogenate naphthenes `and dehydrocyclicize C7 and heavier parafiins without substantial cracking of said paraftins to obtain a low pressure zone effluent comprising hydrogen and C1 and heavier hydrocarbons, separating hydrogen and C1-C5 hydrocarbons from said low pressure zone eiluent to obtain a product containing C7 and heavier hydrocarbons, said product being highly aromatic and boiling in the gasoline range.

2. The method set ionth and described in claim 1 wherein C and C5 hydrocarbons are separated from the high pressure zone and low pressure zone efluents and the separated C5 yand C5 hydrocarbons are isomerized to more highly branched C5 and C5 hydrocarbons of higher octane values.

3. A method of producing high octane gasoline which comprises ractionating a low octane charge stock boiling in the gasoline range to separate an overhead `fraction containing principally C5 and C5 hydrocarbons and a bottoms fraction containing principally C7 and heavier hydrocarbons, reforming said bottoms fraction in the presence of hydrogen yand a reforming catalyst at relatively high pressures of at least 300 p.s.i.g. but below 750 p.s.i.g. and at a temperature in the range 750 to 1050 F. and a space velocity in the range 0.1 to 6 v./hr./v. to crack C10 and heavier hydrocarbons whilst dehydrogenating naphthenes to obtain a high pressure reaction ,zone eluent comprising hydrogen and Cl-lhydrocarbons, separating hydrogen and C1-C5 hydrocarbons from said high pressure zone eiuent to obtain a low pressure zone charge stock comprising principally C7 rand heavier hydrocarbons, reforming said low pressure zone charge stock in the presence of a reforming catalyst and hydrogen at a reaction pressure lower than the aforesaid high pressure and not exceeding 300 p.s.i.g. and reforming conditions of temperature in the range 750 to 1050 F. and space velocity in the range 0.1 to 6 v./hr./v. to dehydrogenate naphthenes yand dehydrocyclicize C7 and heavier parans without substantial cracking of said parains to obtain a low pressure zone eluent comprising hydrogen and C1 and heavier hydrocarbons, separating hydrogen and C1-C5 hydrocarbons from C7 and heavier hydrocarbons to obtain a highly aromatic product boiling in the gasoline range, combining the C5 and C6 hydrocarbons separated Ifrom said loW octane ygasoline with C5 and C6 hydrocarbons produced during reforming Aand isomerizing the combined C5 and C5 hydrocarbons to more highly branched C5 and C@ hydrocarbons of higher octane values,

Beierenccs Cited in the tile of this patent UNITED STATES PATENTS 2,651,597 Corner et al. Sept. 8, 1953 2,703,308 Oblad et al. Mar. l, 1955 2,740,751 Haensel et al. Apr. 3, 1956 2,758,062 Arundale et al. Aug. 7, 1956 2,780,661 Hcmminger et al. Feb. 5, 1957 2,861,037 Hemminger Nov. 18, 1958 ,2,890,163 Lawson June 19, 1959 2,905,619 Sutherland Sept. 22, 1959 2,905,6 21 Bauer et al. Sept. 22, 1959 OTHER REFERENCES Boord: Progress in Petroleum Technology, A.C.S. No. 5, pub. by Am. Chem. Soc., August 7, 1951, Washington, D.C., pp. 364-365.

Patent we.. 3Uoo2,916 l october@ I96I- A corrected below.

PATENTOEEICE y CERTIFICATE "oE CORRECTION Winton W, Hamilton tism'hereby certified that error appears in the above numbered patent requiring correction aludmtlnat` the said Letters Patent should read as CoIumna., "TABLE III", under the headingr T01-,a1 Iow.. ocn ane vSigned and sealed this 15th day of May 1962I (SEAL). Attest:

ERNEST W. SWIDER l DAVID L. LADD Atlestillg Officer v Commissioner of Patents 

1. A METHOD OF PRODUCING HIGH OCTANE GASOLINE WHICH COMPRISES REFORMING LOW OCTANE GASOLINE CONTAINING PRINCIPALLY C7 AND HEAVIER HYDROCARBONS IN THE PRESENCE OF HYDROGEN AND A REFORMING CATALYST AT RELATIVELY HIGH PRESSURES OF AT LEAST 300 P.S.I.G. BUT BELOW 750 P.S.I.G. AND AT A TEMPERATURE IN THE RANGE 750* TO 1050* F. AND A SPACE VELOCITY IN THE RANGE 0.1 TO 6 V./HR/V. TO CRACK C10 AND HEAVIER HYDROCARBONS WHILST DEHYDROGENATING NAPHTHENES TO OBTAIN A HIGH PRESSURE REACTION ZONE EFFLUENT COMPRISING HYDROGEN AND C1+ HYDROCARBONS, SEPARATING HYDROGEN AND C1-C6 HYDROCARBONS FROM SAID HIGH PRESSURE ZONE EFFLUENT TO OBTAIN A LOW PRESSURE ZONE CHARGE STOCK COMPRISING PRINCIPALLY C7 AND HEAVIER HYDROCARBONS, REFORMING SAID LOW PRESSURE ZONE CHARGE STOCK IN THE PRESENCE OF A REFORMING CATALYST AND HYDROGEN AT A REACTION PRESSURE LOWER THAN THE AFORESAID HIGH PRESSURE AND NOT EXCEEDING 300 P.S.I.G. AND REFORMING CONDITIONS 